最快的旅行：盖亚最快恒星的化学标记DR2到恒星晕
The Fastest Travel Together: Chemical Tagging of the Fastest Stars in Gaia DR2 to the Stellar Halo
摘要：
移动最快的恒星提供了深入了解银河系的几个基本属性，包括逃逸速度作为银心半径的函数，总质量，以及恒星与中央超大质量黑洞相遇的性质和频率。盖亚最近发布的第二次数据允许识别具有极高速度的恒星的新样本。化学丰度信息有助于区分这些恒星的可能起源。在这里，我们报告的结果，从我们的高分辨率光谱后续行动，使用阿帕奇点天文台，五个晚型的“超高速”恒星候选人，其特征是总银河系静止帧速度在500-600公里/秒之间，估计有一个大于50%的概率是从银河系中解放出来。我们的新结果证实了Gaia DR 2的径向速度在1 km/s以内。计算了几种主要的恒星大气参数和化学丰度，包括$α$ -元素（Mg，Ti，Si，Ca），Fe-峰元素（Fe，Ni，Co，Cr，Mn），中子俘获元素（Sr，Y，Zr，Ba，La，Nd，Eu）和奇Z元素（Na，Al，K，V，Cu，Sc）。我们发现所有观测到的恒星都是贫金属巨星，其$\leq$ [Fe/H] $\leq$-1 dex为-2，并且在化学上与典型的晕星无法区分。我们的研究结果得到了另外四颗具有极端空间运动的恒星的化学性质的支持，这些恒星是通过现有的光谱测量观察到的。我们的结论是，这些恒星只是恒星晕的高速尾部，有效地排除了来自银河系中心或大麦云云等更奇特的起源。
英文摘要：
The fastest moving stars provide insight into several fundamental properties of the Galaxy, including the escape velocity as a function of Galactocentric radius, the total mass, and the nature and frequency of stellar encounters with the central supermassive black hole. The recent second data release of Gaia has allowed the identification of new samples of stars with extreme velocities. Discrimination among the possible origins of these stars is facilitated by chemical abundance information. We here report the results from our high-resolution spectroscopic followup, using the Apache Point Observatory, of five late-type `hypervelocity' star candidates, characterised by total Galactic rest-frame velocities between 500-600 km/s and estimated to have a probability larger than 50% to be unbound from the Milky Way. Our new results confirm the Gaia DR2 radial velocities to within 1 km/s. We derived stellar atmospheric parameters and chemical abundances for several species including $α$-elements (Mg, Ti, Si, Ca), Fe-peak elements (Fe, Ni, Co, Cr, Mn), neutron-capture elements (Sr, Y, Zr, Ba, La, Nd, Eu) and odd-Z elements (Na, Al, K, V, Cu, Sc). We find that all stars observed are metal-poor giants with -2 $\leq$ [Fe/H] $\leq$ -1 dex and are chemically indistinguishable from typical halo stars. Our results are supported by the chemical properties of four additional stars with extreme space motions which were observed by existing spectroscopic surveys. We conclude that these stars are simply the high-velocity tail of the stellar halo and effectively rule out more exotic origins such as from the Galactic centre or the Large Magellanic Cloud.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
